Chapter 25 continued

Homework1. Lab write up extended for Friday 2. Read and outline pp 521 (beginning with Mass Extinctions) to 530

• Chapter 25 outline will be checked for completion grade tomorrow

3. Quiz tomorrow on Chapter 25 on:• Hypotheses for origin of life on Earth, the sequence of stages for life on earth,

adaptive radiation, and section 25.5

Concept 25.1: Conditions on early Earth made the origin of life possible

• Hypothesis: Chemical and physical processes on early Earth may have produced very simple cells through a sequence of stages:

1. Abiotic synthesis of small organic molecules2. Joining of these small molecules into macromolecules3. Packaging of molecules into protocells4. Origin of self-replicating molecules

Origin of solar system and Earth

Prokaryotes

Atmospheric oxygen

Archaean

4

3

Proterozoic

2

Animals

Multicellular eukaryotes

Single-celled eukaryotes

Colonization of land

Humans

CenozoicMeso-

zoic

Paleozoic

1

Billions of years

ago

Figure 25.7-3

How Rocks and Fossils Are Dated

• Sedimentary strata reveal the relative ages of fossils

• The absolute ages of fossils can be determined by radiometric dating

• A “parent” isotope decays to a “daughter” isotope at a constant rate

• Each isotope has a known half-life, the time required for half the parent isotope to decay

https://www.youtube.com/watch?v=phZeE7Att_s

25.4 Mass Extinctions

• The fossil record shows that most species that have ever lived are now extinct

• caused by changes to a species’ environment

• At times, the rate of extinction has increased dramatically and caused a mass extinction

• The result of disruptive global environmental changes

The “Big Five” Mass Extinction Events

• Five mass extinctions documented in fossil records over the past 500 million years

• In each of the five mass extinction events, more than 50% of Earth’s species became extinct

25

20

15

10

5

0

542 488 444

Era

Period

416

E O S D

359 299

C

251

P Tr

200 65.5

J C

Mesozoic

P N

Cenozoic

0

0

Q

100

200

300

400

500

600

700

800

900

1,000

1,100

Tota

l e

xti

nc

tio

n r

ate

(fa

mil

ies

pe

r m

illi

on

ye

ars

):

Nu

mb

er o

f fa

mili

es:

Paleozoic

145

Figure 25.15

Permian Cretaceous

• The Permian mass extinction occurred in less than 5 million years and caused the extinction of about 96% of marine animal species

• A number of factors might have contributed to these extinctions

• Intense volcanism in what is now Siberia• Global warming resulting from the

emission of large amounts of CO2 from the volcanoes

• Reduced temperature gradient from equator to poles

• Oceanic anoxia from reduced mixing of ocean waters

• The Cretaceous mass extinction 65.5 million years ago separates the Mesozoic from the Cenozoic

• Organisms that went extinct include about half of all marine species and many terrestrial plants and animals, including most dinosaurs

Consequences of Mass Extinctions

1. Mass extinction can alter ecological communities and the niches available to organisms2. It can take from 5 to 100 million years for diversity to recover following a mass extinction3. The percentage of marine organisms that were predators increased after the Permian and Cretaceous mass extinctions4. Mass extinction can pave the way for adaptive radiations

Adaptive Radiations

• Adaptive radiation is the evolution of diversely adapted species from a common ancestor

• Organismal groups form many new species with adaptations specific for different niches

• Adaptive radiations may follow• Mass extinctions• The evolution of novel characteristics• The colonization of new regions

Worldwide Adaptive Radiations

• Mammals underwent an adaptive radiation after the extinction of terrestrial dinosaurs

• The disappearance of dinosaurs (except birds) allowed for the expansion of mammals in diversity and size

• Other notable radiations include photosynthetic prokaryotes, large predators in the Cambrian, land plants, insects, and tetrapods

Close North American relative,the tarweed Carlquistia muirii

KAUAI5.1

million years OAHU

3.7million years

1.3millionyears

MOLOKAI

LANAI MAUI

HAWAII0.4

millionyears

N

Argyroxiphium sandwicense

Dubautia laxa

Dubautia scabraDubautia linearis

Dubautia waialealae

Figure 25.20

Figure 25.20a

KAUAI

OAHU1.3

millionyears

MOLOKAI

LANAI MAUI

HAWAII0.4

millionyears

N

5.1million years

3.7million years

25.5 Major changes in body form can result from changes in sequences and regulation of developmental genes

• Small genetic changes can cause major morphological differences between species

EX: Japanese Euhadra snails, the direction of shell spiral affects mating and is controlled by a single gene

25.5 Major changes in body form can result from changes in sequences and regulation of developmental genes

• Heterochrony- evolutionary change in rate/timing of developmental events

• Organismal shape depends on relative growth rates of different body parts

Example: skeletal structure for bat rings results from increased growth rates of finger bones

25.5 Major changes in body form can result from changes in sequences and regulation of developmental genes

• Altering homeotic genes could lead to major evolutionary changes

• These genes control the placement and arrangement of body parts

• Example: Hox genes, class of genes that instruct cells in a particular location to develop into the correct body structure

Figure 25.24

Hox gene 6 Hox gene 7 Hox gene 8

Ubx

About 400 mya

Drosophila Artemia

Changes in Gene Regulation

• Changes in morphology likely result from changes in the regulation of developmental genes rather than changes in the sequence of developmental genes

• Ex: threespine sticklebacks in lakes have fewer spines than their marine relatives

Concept 25.6: Evolution is not goal oriented

Evolution is like tinkering—it is a process in which new forms arise by the slight modification of existing forms

It is simply the change in allele frequencies, or genetic composition, in populations from generation to generationEvolution can be random or adaptive, in which case, individuals adapt to their specific environment

Evolutionary Novelties

• These structures that evolve to have a new function or have evolved from simple to complex structures

• Ex: simple to complex eyes

Figure 25.26

(a) Patch of pigmented cells (b) Eyecup

Pigmented cells(photoreceptors)

Pigmented cells

Nerve fibersNerve fibers

Epithelium

CorneaCornea

Lens

Retina

Optic nerveOptic nerveOptic

nerve

(c) Pinhole camera-type eye (d) Eye with primitive lens (e) Complex camera lens-type eye

EpitheliumFluid-filled cavity

Cellularmass(lens)

Pigmented layer (retina)